What's ur tank setup? like filter, air pump, gravel etc?
"Cycling the tank" means that you are establishing a bacteria bed in your biological filter to remove the toxins that the fish's metabolism creates.
Cycling is refering to the nitrogen cycle. Beneficial bacteria will feed on the ammonia (which the fish creates, and is toxic to fish) and turn it into nitrite. Then nitrite will turn to nitrate.
It takes 2 weeks for the ammonia spike and another 2 weeks for the nitrite spike then both should go to zero while the nitrates rise, that is when a tank is considered cycled.
People r talking about fishless cycling in which when u set up a new tank, u can put pure ammonia instead of a fish in there to let the tank cycle.
Because ammonia and nitrite r toxic to fish, some fish might die in the cycling process.